This invention relates to an exhaust gas recirculation system of an internal combustion engine, in which a part of the exhaust gas is drawn out from an exhaust pipe and returned to an intake passage, hereinafter simply referred to as EGR system. More particularly, this invention relates to an EGR system having means for controlling an EGR valve, by which means it is possible to keep the actual amount of EGR gas coincide with the optimum amount which is predetermined by experiment.
In order to reduce noxious oxides of nitrogen in exhaust gas to improve engine performance, such as fuel consumption, and engine stability etc., it is necessary to control the amount of EGR gas in conformity with the engine operating condition. Recently, an electronic control system having a memorizing device has been developed. An EGR valve is directly or indirectly controlled by an electric signal from said control system. In the course of development and accomplishment of this electronic control system, a significant problem, that is to say, the problem of what sensors are to be selected for detection engine operating conditions and how to constitute an actuator for controlling an EGR valve, has took place. Known from prior art are a few kind of actuators for controlling an EGR valve. One of these known actuators is a so-called butterfly valve type system in which an EGR valve is directly driven by a pulse motor and the like. A feed back system is also known, in which a diaphragm type EGR valve is driven with positive pressure which is controlled through bleeding it to the atmosphere by means of a solenoid valve, a position sensing device attached to the EGR valve senses the valve opening position thereof and, then, the opening position of the EGR valve is feedback controlled by comparing it with a memorized valve.
The butterfly valve type system using a pulse motor or the like is, however, lacking in responsiveness and heat resistivity, because the EGR valve must control EGR gas, which has a high temperature, generates pulsatory motion and contains fine particles, fine water moisture and the like. Therefore, the EGR valve requires significantly strict conditions concerning controllability, heat resistivity, durability and the like. The feedback EGR valve control system having a position sensing device is bulky due to mounting of the position sensor thereon and also lacking in resistivity to heat and vibration.
An object of the present invention is to provide an EGR system of an internal combustion engine which obviates the disadvantage mentioned above.
An another object of the present invention is to provide an EGR system of an internal combustion engine in which a mechanical valve, particularly a diaphragm valve as its original construction or its minor modified construction, is used as an EGR valve for directly controlling EGR gas, and in which, in order to actuate said diaphragm valve, a pressure modulating valve is also provided in a pipeline for introducing positive or negative pressure into said diaphragm valve, so that, by means of said pressure modulating valve, the positive or negative pressure being introduced into said diaphragm valve is bled into the atmosphere in accordance with the electrical signal from a control device.